1. Field of the Invention
The present invention relates to a method of manufacturing a vertical light emitting diode (LED), which can prevent the damage of a light emitting structure during an LLO (laser lift-off) process for removing a sapphire substrate.
2. Description of the Related Art
Generally, a nitride-based semiconductor LED is grown on a sapphire substrate, but the sapphire substrate is a rigid nonconductor and has poor thermal conductivity. Therefore, there is a limitation in reducing the manufacturing costs by reducing the size of a nitride-based semiconductor LED, or improving the optical power and chip characteristic. Particularly, because the application of a high current is essential for achieving high power LED, it is important to solve a heat-sink problem of the LED. To solve this problem, there has been proposed a vertical LED in which a sapphire substrate is removed using an LLO technique.
Now, a conventional method of manufacturing a vertical LED will be described with reference to FIGS. 1A to 1F.
FIGS. 1A to 1F are process diagrams sequentially showing a conventional method of manufacturing a vertical LED.
First, as shown in FIG. 1A, a light emitting structure 110 is formed on a transparent substrate 110 such as sapphire. The light emitting structure 110 includes an n-type nitride semiconductor layer 112, a GaN/InGaN active layer 114 with a multi-quantum well structure, and a p-type nitride semiconductor layer 115, which are sequentially laminated.
As shown in FIG. 1B, photoresist patterns PR for defining a desired size of unit LED elements are formed on the p-type nitride semiconductor layer 115.
Subsequently, as shown in FIG. 1C, the light emitting structure 110 is isolated into unit LED elements through an ISO (isolation) process using dry etching such as ICP (inductive coupled plasma) or layer, with the photoresist patterns being set to an etching mask. Then, the photoresist patterns are removed.
Although not shown, after the light emitting structure 110 is isolated into unit LED elements, an insulating film or reflecting film may be formed on the side surfaces of the isolated light emitting structures 110. The insulating film or reflecting film can be omitted depending on the characteristics of LED and process conditions.
Next, as shown in FIG. 1D, a p-electrode 140 is formed on each of the isolated light emitting structures 110. Then, as shown in FIG. 1E, a structure support layer 160 is formed on the p-electrode 140.
Subsequently, as shown in FIG. 1F, the substrate 110 is removed through the LLO process. In the LLO process, when an energy of about 700 mJ/cm2 is applied at the normal temperature in an arrow direction, the energy is absorbed at the interface between the substrate 100 and the light emitting structure 110 such that the bonded surface of the light emitting structure 110 is thermally discomposed, and the substrate 100 and the light emitting structure 110 are then separated from each other.
Then, although not shown, an n-electrode is formed on each of the n-type nitride semiconductor layers 112 which are exposed by the removing of the substrate, thereby forming vertical LEDs.
In the conventional method of manufacturing a vertical LED, when the LLO process for removing the substrate is performed, cracks occur at the edge of the light emitting structure 100, as indicated by ‘A’ in FIG. 2. Then, defects may occur in the LED. FIG. 2 is a photograph showing the problem of the vertical LED manufactured according to the conventional method.
Further, a crack may also occur in the insulating film or reflecting film formed on the side surfaces of the isolated light emitting structures or the adhesion therebetween may be degraded during the LLO process.
Therefore, when a vertical LED is manufactured according to the conventional method, the characteristic and reliability of the vertical LED are degraded because of the above-described problems.